Alzheimer's disease (AD) is a progressive and irreversible brain disorder with no known cure. A small protein, amyloid beta peptide (Abeta) containing 39-43 amino acids, is widely considered a culprit for the disease. Recent evidence indicates that soluble oligomers of Abeta may represent the primary toxic species of amyloid in AD. It is accepted that newly produced Abeta is monomeric, soluble and non-toxic, adopting random coil/alpha-helix mixture structures under normal physiological conditions. In AD, Abeta undergoes conformational changes from random coil/alpha-helix to beta-sheet structure, resulting in oligomerization and precipitation. In search of a compound that blocks this conformational change, we discovered that a class of tricyclic pyrones (TP), especially CP2 (code name), prevents the death of human neuroblastoma MC65 cells related to intracellular accumulation of Abeta-containing metabolites. CP2 inhibits the aggregation of Abeta 1- 40 and Abeta1-42 peptides, blocks Abeta1-40 and Abeta1-42 beta-sheet formation, and binds to Abeta peptides in vitro. CP2 also penetrated blood-brain barrier in mice. These exciting results suggest that CP2 may potentially serve as a drug to treat AD. We propose the following specific aims: (1) Studies of the structural changes and aggregation states of Abeta40 and Abeta42 in the presence of CP2 and analogs;(2) Identification of the mechanism by which CP2 blocks beta-sheet formation and aggregation of Abeta40 and Abeta42;(3) Syntheses of a small library of TP, new analogs of CP2 containing functional groups at C9, C11 and C14;(4) Studies of the in vitro bioactivities of CP2 analogs in cell cultures;and (5) Studies of the in vivo pharmacological effect of CP2 analogs with 3xTg-AD APP mice. The ultimate goal of this proposal are to identify a lead compound that is able to block the formation of Ab lesions in animal model, which may lead to drugs for the treatment of AD. CP2 and its analogs should have great potential in AD drug development. Relevance: Oligomerization of amyloid beta-peptide has been shown to be a major feature of the pathogenesis of AD. Monomeric Abeta is produced during normal metabolism and appears to have no toxic effects on neurons. However, soluble oligomeric Abeta showed high neuronal toxicity. Inhibition of the formation of these toxic soluble Abeta oligomers would provide therapeutics for AD.